KR100803771B1 - Process for the preparation of molecular sieve adsorbent for selective adsorption of oxygen from air - Google Patents

Abstract

The present invention relates to the preparation of molecular sieve adsorbents selective for oxygen from argon and / or a gas mixture of nitrogen and oxygen. More specifically, the present invention relates to the preparation of molecular sieve adsorbents useful for the separation of oxygen-argon gas mixtures. More specifically, the present invention relates to the preparation and use of molecular sieve adsorbents by cation exchange in zeolites with rare earth cations, obtaining an oxygen selective adsorbent from nitrogen and a gas mixture of argon and oxygen at ambient conditions of temperature and pressure. will be. Thus, the prepared adsorbents are useful for the separation and purification of nitrogen and argon from mixtures of oxygen with nitrogen and argon.

Molecular sieve, adsorbent, oxygen, zeolite, rare earth, selective

Description

Process for the preparation of molecular sieve adsorbent for selective adsorption of oxygen from air

The present invention relates to a process for the preparation of molecular sieve adsorbents for the selective adsorption of oxygen from air. The invention also relates to the use of zeolites exchanged with rare earths as selective adsorbents for the separation of gases with closely related physical properties. More specifically, the present invention relates to the preparation and use of adsorbents selective for oxygen from a gas mixture of argon and oxygen.

The use of adsorption techniques to separate one gas component from a gas stream was initially developed to remove carbon dioxide and water from the air. Gas adsorption techniques are currently used in processes for the recovery of hydrogen from mixtures of hydrocarbons and hydrogen, and the concentration of oxygen from air.

Four widely used types of adsorbents include activated carbon, zeolite molecular sieves, silica gel, and activated alumina. Carbon molecular sieve (CMS), which exhibits a very narrow pore size distribution and promotes separation of air to recover nitrogen, provided a safe and growing market for carbon molecular sieves.

Adsorption processes for the separation of oxygen and argon from air have been increasingly used for commercial purposes over the last 30 years. Oxygen requirements in sewage treatment, fermentation, cutting and welding, fish farming, electric furnaces, pulp bleaching, glass blowing, and medical purposes, especially in the steel industry, where the required oxygen purity is between 90 and 95% This is best met by an adsorption based pressure swing or vacuum swing process. At present, it is estimated that about 20% of global oxygen demand is met by adsorptive separation of air. However, the maximum achievable purity by the adsorption process is approximately 95% due to the separation of 0.934 mol% argon present in the air which is the limiting factor in achieving 100% oxygen purity. Moreover, the production of oxygen from air based on adsorption is economically uncompetitive over cryogenic fractionation of air for more than 200 tonnes of operation per day.

Argon gas is mainly used in industry as an inert gas to create an inert atmosphere. Argon or argon-hydrogen mixtures are used for the production of high purity iron. Argon is also used for welding, cutting, and spraying of metals, and depending on the welding process, this rare gas is used purely, as a mixture, or in combination with oxygen, hydrogen, or carbon dioxide. An argon / argon-hydrogen mixture (> 5% H ₂ ) is used as the protective gas for plasma welding. There are many potential applications of argon and this study is expected to lead to increased argon consumption in the future.

In the case of adsorbents used in adsorptive separation processes, there are two important properties that need to be considered in assessing their potential: adsorption capacity and adsorption selectivity. The adsorption capacity of the adsorbent is defined as the amount in terms of volume or weight of the adsorbent. The higher the capacity of the adsorbent for the desired component, the better because it increases the adsorption required to separate a particular amount of one component from a particular concentration of mixture. This reduction in the amount of adsorbent in certain adsorption processes reduces the cost of the separation process.

Adsorption selectivity of one component to another is calculated as the ratio of gas volumes adsorbed at a given pressure and temperature. The adsorption selectivity of one component is due to, for example, a steric effect when the adsorption isotherms of the components of the gas mixture are noticeably different and a kinetic effect when the components have substantially different adsorption rates. effect).

Adsorption for oxygen and nitrogen production is widely used, and tremendous research efforts are being made to improve the adsorption process for higher adsorption capacity and selectivity. The adsorbent affects separation by strongly adsorbing one or more components of the mixture than the other components present in the mixture.

The various interacting forces involved in the adsorption process are van der Waals interactions, acid-base interactions, hydrogen bonding, electrostatics, chelation, and clathration. Thus, the adsorbents are appropriately modified to improve the interaction between the adsorbent and adsorbate molecules to improve the adsorption capacity and selectivity. Zeolites, crystalline inorganic porous materials with molecular sized pores, have been widely used for adsorptive separation. Since the excess skeletal cations of zeolites are moderately fluid, cation exchange in zeolites is one of the most common techniques of use for surface modification of cations of suitable size and charge to enhance zeolite adsorbate interactions. The literature on adsorbent development studies carried out on zeolites shows that most reported studies are limited to alkali and alkaline earth cations as redundant skeletal cations. Adsorption of nitrogen, oxygen, and argon is rarely reported in zeolites having bivalent or higher cations. Because trivalent cations have greater charge densities, if these cations are present in positions accessible to the nitrogen molecule, they will have greater electrostatic interaction with the nitrogen molecule.

The main property of the separation, removal, or concentration of oxygen, nitrogen, and argon from air is that there is no cost for starting materials, which are typically air. The cost of the desired gas to be produced or removed depends essentially on the other factors below.

(a) the cost of the apparatus necessary to separate or concentrate the gas,

(b) the energy costs required to operate the device,

(c) The cost of additional purification steps to be considered when gas with high purity is required.

In view of these factors, various economically advantageous processes have been proposed so far. Such processes include a process in which air is liquefied at low temperatures to separate oxygen or nitrogen using, for example, a boiling point difference between liquid oxygen (-182.9 ° C.) and liquid nitrogen (−195.8 ° C.). The apparatus used is suitable for producing large amounts of oxygen and nitrogen based on this method. Disadvantages of the process are that it requires a large amount of power, a large device is location-specific, very portable, and takes hours to start and stop the plant. Over the past two decades, adsorption and membrane based processes for the separation of oxygen and nitrogen from air have emerged as possible alternatives.

Membrane systems were used to separate oxygen and nitrogen from air. U.S. Patent No. 5,091,216 (1992) to Hayes et al., U.S. Patent No. 5,004,482 (1991) to Haas et al., And U.S. Patent Application No. 2,038,62 to Katz et al. (2002) discloses the separation of oxygen and nitrogen from air using polymeric form membranes. Membrane based systems operate at very high pressures. The main disadvantage of this method is that the thin polymer membrane is too weak to maintain the high gas pressure differential required for separation, resulting in only about 50% purity of the product gas.

In the prior art, selective adsorbents for nitrogen from oxygen and mixtures of argon and nitrogen have been reported [Reiss U.S. Patent 5,114,440 (1992)], Coe et al. U.S. Patent 4,481,018 (1984), Sircar et al. Patent 4,557,736, Chao, Chien-Chung, U.S. Patent 4,859,217 (1989), Coe et al., US Patent 5,152,813 (1992), Chao, Chien-Chung, U.S. Patent 5,174,979 (1992), Chao, Chien-Chung, United States Patent 5,454,857 (1995), US Patent 5,464,467 (1995) by Fitch et al., US Patent 5,698,013 (1997) by Chao, Chien-Chung, US Patent 5,868,818 (1999) by Ogawa et al., US Patent 6,030,916 by Choudary et al. (2000), US Patent 4,964,889 (1990) to Chao, Chien-Chung, Gerhard, US Patent 4,943,304 (1990) to Coe et al., And US Patent 6,231,644 (2001) to Jain. In the adsorbents, A type zeolite, faujasite, clinoptilolite, chabazite, and monolith, respectively, were used. Efforts have been reported to improve adsorption capacity and selectivity by exchanging excess skeletal cations with alkali and / or alkaline earth metal cations to increase the number of excess skeletal cations of the zeolite. Adsorption selectivity to nitrogen was also substantially improved by exchanging the zeolite with cations such as lithium and / or calcium in the faujasite form zeolite. These adsorbents have been used in processes for the separation or concentration of oxygen by selectively removing nitrogen from air. The disadvantage of these adsorbents is about 95% maximum oxygen purity achievable by the adsorption process because the separation of 0.934 mole percent argon present in air is a limiting factor in achieving 100% oxygen purity. These adsorbents are also very sensitive to moisture so that the adsorption capacity and selectivity will decrease with the presence of moisture.

U.S. Patent 4,453,952 (1984) to Izumi et al. Discloses the preparation of oxygen selective adsorbents by replacing the sodium cations of zeolite A with K and Fe (II). The adsorbent only shows oxygen selectivity at low temperatures and its preparation requires the exchange of iron and subsequent potassium exchange carried out at about 80 ° C. using an aqueous salt solution of metal ions. A disadvantage of this invention is that potassium exchange in zeolite leads to lower thermal and hydrothermal stability of the adsorbent.

U.S. Patent No. 3,979,330 to Munzner et al. Discloses the preparation of carbon-containing molecular sieves wherein coke containing up to 5% of volatile components is treated at 600-900 ° C to remove carbon from hydrocarbons. The released carbon is deposited in the carbon framework of the coke to narrow existing pores. The disadvantage of this process is that the deposition on the carbon skeleton is not uniform and is a very energy intensive process.

US Pat. No. 4,742,040 to Ossaki et al. Discloses charcoal powders containing a small amount of coal tar as binders, pelletizing, carbonizing, washing in acid solutions for removal of soluble components, specific amounts of creosote Disclosed is a process for preparing carbon molecular sieves with increased adsorption capacity and selectivity by addition of creosote or other aromatic compounds, heating at 950-1000 ° C., and cooling in an inert gas. The disadvantage of this process is that it is energy intensive and complex and the organic compounds are expensive.

U.S. Patent No. 4,880,765 to Knoblauch et al. Discloses uniform treatment by narrowing the pores present by treating the carbonaceous product in multiple stages with inert gas and steam in a vibration oven and then further treating it with benzene at high temperature. A process for producing a carbon molecular sieve having quality and good separation properties is disclosed. The production of carbon molecular sieves is a multi-step process with extreme care at each stage to obtain fully reproducible carbon molecular sieves. Moreover, the process is a very high temperature process resulting in higher product costs.

US Pat. No. 5,081,097 (1992) to Sharma et al. Discloses a copper modified carbon molecular sieve for the selective removal of oxygen from air. The molecular sieve is prepared by forming an sorbent precursor by pyrolysis of a mixture of a copper containing material and a polyfunctional alcohol. The adsorbent precursor is then heated and reduced to produce carbon molecular sieves modified with copper. Pyrolysis is a high temperature process that makes the entire process of adsorbent manufacture an energy intensive process.

Schoudary et al., US Pat. No. 6,087,289 (2000), discloses a process for preparing zeolitic adsorbents containing cerium cations for the selective adsorption of oxygen from gas mixtures. Cerium exchange to zeolite is carried out under reflux conditions using an aqueous solution of cerium salt at about 80 ° C. for 4 to 8 hours, repeated 2-3 times in an ion exchange process, and separation of gases is carried out at very low pressure ranges. It is studied by chromatography. The main disadvantage of this adsorbent is the oxygen selectivity obtained only in the low pressure range. Moreover, adsorption was only studied by gas chromatography in a limited pressure range. Thus, no higher pressure range adsorption data was obtained.

In another approach, chemical vapor deposition techniques have been used to control the pore opening size of zeolites by precipitation of silicon alkoxides [M. Niwa et al., JCS Farady Trans. I, 1984, 80, 3135-3145; M. Niwa et al., M. Niwa et al., J. Phys. Chem., 1986, 90, 6233-6237; Chemistry Letters, 1989, 441-442; M. Niwa et al., Ind. Eng. Chem. res., 1991, 30, 38-42; D. Ohayon et al., Applied Catalysis A-General, 2001, 217, 241-251. Chemical vapor deposition is performed by taking the required amount of zeolite in a glass reactor, which is thermally activated at 450 ° C. in-situ under an inert gas such as a nitrogen flow. The vapor of the silicon alkoxide is continuously injected into an inert gas stream, which carries the vapor to the zeolite surface where the alkoxide chemically reacts with the silanol groups of the zeolite. Once the desired amount of alkoxide is deposited on the zeolite, the sample is heated to 550 ° C. in air for 4-6 hours and then dropped to ambient temperature and used for adsorption. The main drawbacks of this technique are that (i) chemical vapor deposition leading to non-uniform coating of alkoxides results in non-uniform pore inlet closure, and (ii) the process must be carried out at increased temperatures where alkoxides are likely to vaporize.

Bligh et al., US Pat. No. 4,239,509 (1980), describes the steps of reducing the amount of nitrogen in the raw material argon between traces and 0.15% by volume to separate oxygen and argon and reducing the residual oxygen and argon with residual nitrogen. Disclosed is a method for purifying raw material argon containing argon, oxygen, and nitrogen, which comprises passing through 4A molecular sieve to separate oxygen and argon. All remaining oxygen and nitrogen must pass through a volume of 4A molecular sieve at or below -250F as a whole. The disadvantage of this process is that the adsorption process is carried out at -157 ° C (-250F) temperature, and the arrangement of the device is complicated for very low temperature separation, which is economically unacceptable.

Kumar et al., US Pat. No. 4,447,265 (1984), describes the kinetics for passing mixed gas through an adsorbent bed with thermodynamic selectivity for adsorption of nitrogen and then the unadsorbed portion retaining oxygen. Vacuum vibration adsorption (VSA) through a second adsorbent bed with kinetic selectivity initiates the separation of argon from a gas stream comprising argon in a mixture of oxygen and nitrogen. Both adsorbent beds are regenerated by vacuum desorption, which vacuum desorption is applied to the first bed for a longer time than the second bed. The mixed gas stream supplied to the VSA unit may be from the raw argon column associated with the cold air separation plant, and the waste gas from the VSA unit may be recycled to the main column of the cold air separation plant, thus improving argon recovery. You can. The disadvantage of this process is that the regeneration of the adsorbent is a time consuming process and also requires a low temperature unit to recover more argon, otherwise the recovery is low.

Hayashi et al., US Pat. No. 4,529,412 (1985), discloses a process for obtaining high purity argon from air by pressure-vibration-adsorption. Air is initially passed through a adsorption mechanism packed with zeolite molecular sieves, and then through an adsorption mechanism packed with carbon molecular sieves, and then subjected to a pressure-vibration-adsorption operation to simultaneously obtain concentrated argon and high purity oxygen. The disadvantage of this process is that adsorptive beds are required and the process takes longer. In addition, two beds need to be manufactured in the process, thus increasing the manufacturing cost.

Agrawal et al., US Pat. No. 4,817,392 (1989), discloses a process for the preparation and recovery of O ₂ deficient argon streams from gas mixtures containing argon and oxygen. The argon containing gas mixture is initially processed in a low temperature separation unit to produce a raw argon stream having an argon concentration between 80 and 90%. The raw argon stream is then passed to a membrane based separation unit where it is separated to produce an O ₂ deficient argon stream and an O ₂ rich stream. The O ₂ rich stream is recycled to a low temperature separation unit and the Ar deficient oxygen stream is recovered as a product or further purified. The disadvantage of this process is that it requires membrane based separation, thus increasing the manufacturing cost.

US Pat. No. 5,557,951 to Prasad et al. Discloses a device for producing high purity product grade argon from an argon containing stream using a low temperature argon column in combination with a solid electrolyte ion or mixed conductor membrane. The disadvantage of this process is that the recovery of argon can be achieved by two processes-one at low temperature and the other at membrane separation, thus increasing the manufacturing cost.

Chen et al., US Patent RE 34, 595 (1994), discloses an argon gas stream, in particular an argon gas stream obtained by cryogenically separating air and filtering oxygen from argon by selective permeation of oxygen through the membrane. Disclosed is a purification method. In this process, the argon gas is heated and compressed and then permeated through the solid electrolyte membrane which is selective for the permeation of oxygen in preference to the other components of the gas. Purified argon may then be distilled to remove other components such as nitrogen. A process for the production of a purified argon stream is provided in which oxygen and nitrogen are removed from the raw bulk argon stream, especially the argon stream produced by low temperature, adsorption, or membrane separation of air. The process separates a heated and compressed raw argon stream containing nitrogen and oxygen into an oxygen permeate stream and an oxygen depleted argon stream by passing the compressed and heated argon stream through a solid electrolyte membrane that is selective for the transmission of oxygen. It includes a step. The oxygen depleted argon stream is then fed to a distillation column to separate nitrogen from the oxygen depleted argon stream to form a purified argon stream and a nitrogen waste stream.

It is an object of the present invention to provide a process for the preparation of molecular sieve adsorbents for the selective adsorption of oxygen from air, which can obviate the aforementioned disadvantages.

Another object of the present invention is to provide an oxygen selective zeolitic adsorbent.

It is a further object of the present invention to provide an adsorbent which can be prepared by exchanging rare earth cations in zeolite X, in particular cerium, europium, and gadolinium.

Another object of the present invention is to provide an oxygen selective adsorbent by simple post-synthesis modification of zeolite X.

Another object of the present invention is to provide an adsorbent that can be regenerated by the desorption of oxygen by adjusting the equilibrium adsorption pressure.

It is a further object of the present invention to provide an adsorbent which has a high selectivity for oxygen relative to argon and can be commercially available for the separation and purification of argon.

The present invention provides a process for the preparation of molecular sieve adsorbents for the selective adsorption of oxygen from air by exchanging the powder and pellet forms of sodium zeolite X with aqueous solutions of rare earth cations such as cerium, europium, and gadolinium at increased temperatures. . Dry zeolite X containing 20 to 95% rare earth cations in total exchangeable sodium cations was subjected to oxygen, using a static volumetric system of adsorption apparatus (Model ASAP 2010) supplied by Micrometrics Corporation USA after activation at high temperature and vacuum. Adsorption studies on nitrogen, and argon were made. Adsorption capacities and selectivities of zeolites exchanged with rare earths for oxygen, nitrogen, and argon were measured at 15 ° C. and pressure ranges from 0.5 to 760 mmHg. From these data, adsorption isotherms were drawn and pure component selectivity of the gases was calculated. The present invention provides a process for preparing zeolite adsorbents having selectivity to oxygen in preference to nitrogen and argon.

Accordingly, the present invention provides a process for preparing a molecular sieve adsorbent for the selective adsorption of oxygen from air, the process comprising the following steps:

(i) exchanging zeolite X in powder or pellet form with a water-soluble salt of a rare earth metal selected from the group consisting of cerium, europium, gadolinium, and any mixtures thereof;

(ii) filtering the mixture and washing the powder or pellet with hot distilled water until the anion is gone to obtain the exchanged zeolite;

(iii) drying the exchanged zeolite; And

(iv) activating the exchanged zeolite.

In one embodiment of the present invention, zeolite X in powder form and spherical pellet form with 100% crystallinity can be used for the preparation of surface modified molecular sieve adsorbents.

In another embodiment of the present invention, the Na cation of the zeolite was exchanged with 10 to 100 equivalent percentages (cerium, europium, and gadolinium) or salts supplied with any water soluble salts of chloride, nitrate and acetate salts.

In another embodiment of the invention, the cation exchange may be performed at a temperature in the range of 30 to 90 ° C. for a range of 4 to 8 hours.

In another embodiment of the present invention, cation exchange may be performed at a cation concentration in the range of 0.01 to 0.1M solution.

In another embodiment of the present invention, the exchanged zeolite may be dried in a temperature range of 20 to 80 ° C. under air or vacuum conditions.

In another embodiment of the present invention, the exchanged zeolite can be activated at a temperature range of 350 to 450 ° C. for a period of 3 to 6 hours and then cooled under inert or vacuum conditions.

1 shows adsorption isotherms of nitrogen, argon, and oxygen at 15 ° C. on zeolite X pellets.

2 shows adsorption isotherms at 15 ° C. of nitrogen, argon, and oxygen on zeolite X pellets exchanged with cerium.

3 shows adsorption isotherms at 15 ° C. of nitrogen, argon, and oxygen on zeolite X pellets exchanged with europium.

4 shows adsorption isotherms of nitrogen, argon, and oxygen at 15 ° C. on zeolite X pellets exchanged with gadolinium.

The present invention provides a process for the preparation of an oxygen selective adsorbent having an oxygen adsorption selectivity prior to nitrogen and argon. Moreover, these adsorbents show greater interactions with oxygen as compared to nitrogen and argon when observed from the thermal adsorption values determined in Henry region I.

Zeolites, microporous crystalline aluminosilicates, are increasingly being used as adsorbents to separate mixtures of compounds with closely related molecular properties.

Properties that make zeolites attractive for separation generally include high thermal and hydrothermal stability, uniform pore structure, easy pore pore changes, and even significant adsorption capacity at low adsorbate pressures. Moreover, zeolites can be prepared synthetically under relatively mild hydrothermal conditions.

Zeolite NaX powder and pellets [Na ₈₆ (AlO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ wH ₂ O] are used as starting materials. X-ray diffraction data showed that the starting material was highly crystalline. Known zeolite NaX powder and pellet [Na ₈₆ (AlO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ wH ₂ O] were a two liter round bottom flask with zeolite X to rare earth solution ratio 1:80 at 80 to 120 ° C. for 4 hours. It was refluxed with 0.01 M rare earth (Ce, Eu, and Gd) acetate and chloride solutions taken at. Zeolite samples with different amounts of rare earths were prepared by adding repeated rare earth cation exchange to the zeolites. The zeolite sample was filtered after reflux and washed with distilled water until free of chloride when tested by AgNO ₃ solution. In the case of acetate, an over wash was done with hot water (60 ° C.). The degree of rare earth exchange to zeolite X is determined from the concentration of rare earth cations in the original solution and the filtrate. Rare earth cations were analyzed by using a 0.01 M EDTA solution containing sodium acetate buffer at pH = 6 and containing xylenol orange tetra sodium salt indicator.

Oxygen, nitrogen, and argon adsorption at 15 ° C. was activated using a sample at 350 to 450 ° C. under vacuum for 4 to 8 hours as described in the Examples, followed by using a static volumetric system (Micrometrics, USA. ASAP 2010). Was measured. The addition of the adsorbate gas was at the volume required to achieve the target pressure set from 100 to 760 mmHg. A minimum equilibrium interval of 5 seconds was used to determine the equilibrium for each measurement point.

The pure component selectivity of one gas to another (A and B) was determined by the formula:

α _{A / B} = [V _A / V _B ] _{P, T}

Where V _A and V _B are the volumes of gases A and B adsorbed at equilibrium pressure P and temperature T.

Structural analysis of zeolite samples was determined from the well-defined peak intensities at 2θ (theta) values of 6, 10, 11, 8, 15.5, 20, 23.4, 26.8, 30.5, 31, 32, and 33.8. It was performed by X-ray diffraction. X-ray powder diffraction was measured using a PHILIPS X'pert MPD system equipped with an XRK 900 reaction chamber.

Important inventive steps related to the present invention include: (i) Oxygen in the zeolite pupil by forming a non-stoichiometric oxide of cerium / uropium / gadolinium which interacts with the oxygen molecules in addition to the exchange with an aqueous lanthanide solution and cation exchange A process for the formation of selective species, i.e. molecular sieve adsorbents, and (ii) a novel technique for introducing metal oxides specific to the adsorbate into the micropores of zeolites to develop new adsorbents in addition to conventional cation exchange. . Non-stoichiometric oxides of these rare earths, such as cerium and europium, can react reversibly with oxygen and act like adsorption with the aid of chemisorption by reversibly changing the oxidation state. In addition, the high heat of the observed adsorption indicates an interaction of chemisorption forms with oxygen molecules.

The adsorption capacity of the catalyst was chosen to adsorb nitrogen, oxygen, and argon gas on an exchanged zeolite having a purity of 99.9% at 15 ° C. and a pressure range of 0.5 to 800 mmHg, followed by adsorption of gases at 15 ° C. and pressures of 100 and 760 mmHg. Evaluated and demonstrated by calculating degrees.

The following examples are given for illustration only and therefore should not be construed as limiting the scope of the invention.

Example -One

1.0 gm of zeolite NaX pellet, [Na ₈₆ (AIO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ wH ₂ O], was activated at 350 ° C. under a vacuum of 10 ⁻³ mmHg and the adsorption measurement was run at 760 mmHg with an equilibrium interval of 5 seconds. The measurement system (Micrometrics ASAP 2010C) was used for N _{2 ,} O _{2 ,} and Ar with a purity of 99.9% at 15 ° C. Adsorption capacities for N _{2 ,} O _{2 ,} and Ar are 9.74 cc / g, 3.31 cc / g, and 3.29 cc / g, respectively, at a temperature of 15 ° C. and a pressure of 760 mmHg. The selectivity of nitrogen to oxygen at 15 ° C. and a pressure of 760 mmHg was 2.9; The selectivity of nitrogen to argon was 2.96 and the selectivity of oxygen to argon was 1.0.

Example -2

25.0 g of molecular sieve NaX pellets were exchanged with 0.301 M cerium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquor was free of acetic acid ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 25% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.17 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. Adsorption capacity for oxygen was 2.4 cc / g at 15 ° C. temperature and 760 mmHg pressure, oxygen selectivity to argon was 1.0, nitrogen selectivity to oxygen was 3.3, and nitrogen to argon at 100 mmHg pressure The selectivity of was 3.3.

Example -3

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M cerium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetic acid ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 84% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 1.4 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. Adsorption capacity for oxygen was 3.7 cc / g at 15 ° C. temperature and 760 mmHg pressure, oxygen selectivity for argon was 8.0, nitrogen selectivity to oxygen was 0.4, and nitrogen to argon at 100 mmHg The selectivity of was 3.5.

Example -4

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M cerium chloride solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash was free of chloride ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 28% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.58 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. Adsorption measurements were carried out at a temperature of 15 ° C. and a pressure of 760 mmHg with an oxygen selectivity of 3.0 for argon at a pressure of 100 mmHg, a selectivity of nitrogen to oxygen of 1.3 and a selectivity of nitrogen to argon of 4.0.

Example -5

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M cerium chloride solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash was free of chloride ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 93% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.53 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. The adsorption capacity for oxygen was 3.1 cc / g at 15 ° C. temperature and 760 mmHg pressure, the selectivity of oxygen to argon was 3.5, the selectivity of nitrogen to oxygen was 1.4 and the nitrogen to argon at pressure of 100 mmHg The selectivity of was 5.0.

Example -6

25.0 g of molecular sieve NaX powder was exchanged with 0.014 M cerium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 74% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.13 gm. The adsorption capacity for oxygen was 4.6 cc / g at 15 ° C. temperature and 760 mmHg pressure, the selectivity of oxygen to argon was 4.0, the selectivity of nitrogen to oxygen was 1.1, and the nitrogen to argon at 100 mmHg pressure. The selectivity of was 4.2.

Example -7

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M cerium acetate solution at a ratio of 1:80 and refluxed at 50 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 20% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.22 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. Adsorption capacity for oxygen was 2.2 cc / g at 15 ° C. temperature and 760 mm Hg pressure, oxygen selectivity for argon was 1.5, nitrogen selectivity to oxygen was 2.2, and nitrogen to argon at 100 mmHg pressure The selectivity of was 3.2.

Example -8

25.0 g of molecular sieve NaX pellets were exchanged with 0.1 M cerium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The cerium content in the dry zeolite amount was 30% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.15 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. The adsorption capacity for oxygen was 3.2 cc / g at 15 ° C. temperature and 760 mm Hg, the selectivity of oxygen to argon was 2.0, the selectivity of nitrogen to oxygen was 2.4, and the selection of nitrogen to argon at 100 mmHg pressure. Degree was 3.8.

Example -9

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M europium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The europium content in the dry zeolite amount was 52% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.59 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. The adsorption capacity for oxygen was 2.3 cc / g at 15 ° C. temperature and 760 mm Hg, the selectivity of oxygen to argon was 1.7, the selectivity of nitrogen to oxygen was 1.1, and the selection of nitrogen to argon at 100 mmHg pressure. Degree was 2.7.

Example -10

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M europium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The europium content in the dry zeolite amount was 67% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.52 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. Adsorption capacity for oxygen was 2.6 cc / g at 15 ° C. temperature and 760 mmHg, oxygen selectivity to argon was 2.3, nitrogen selectivity to oxygen was 1.3, and nitrogen selection to argon at 100 mmHg pressure Fig. 3.1.

Example -11

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M gadolinium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The gadolinium content in the dry zeolite amount was 82% of the total replaceable sodium cations. This zeolite was activated at 35 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.59 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. The adsorption capacity for oxygen was 3.2 cc / g at 15 ° C. temperature and 760 mm Hg, the selectivity of oxygen to argon was 4.0, the selectivity of nitrogen to oxygen was 1.3, and the selection of nitrogen to argon at 100 mmHg pressure. The degree was 5.0.

Example -12

25.0 g of molecular sieve NaX pellets were exchanged with 0.01 M gadolinium acetate solution at a ratio of 1:80 and refluxed at 80 ° C. for 4 hours. This hot solution was filtered, washed with hot distilled water until the wash liquid was free of acetate ions and dried in air at room temperature (28 ° C.). The gadolinium content in the dry zeolite amount was 88% of the total replaceable sodium cations. This zeolite was activated at 350 ° C. under vacuum (10 ⁻³ mmHg) and the weight of the sample after activation was 0.66 gm. Adsorption measurements were performed at a temperature of 15 ° C. and a pressure of 760 mm Hg. The adsorption capacity for oxygen was 2.8 cc / g at 15 ° C. temperature and 760 mm Hg, the selectivity of oxygen to argon was 2.0, the selectivity of nitrogen to oxygen was 3.0, and the selection of nitrogen to argon at 100 mmHg pressure. Fig. 6.0.

The main advantages of the present invention are as follows:

1. The adsorbents prepared by the modification of zeolite X show oxygen selectivity over nitrogen and argon.

2. A simple exchange with an aqueous solution of rare earth cations is used for the preparation of the adsorbent.

3. The exchange is carried out at 80 ° C. and atmospheric pressure.

4. The adsorbent is very easy to handle.

5. The adsorbent shows nearly 8 oxygen / argon selectivity in the low pressure range studied.

6. Adsorbents are useful for commercial separation and purification of oxygen and argon from mixtures with nitrogen.

7. Adsorbents are useful for chromatographic separations of oxygen, nitrogen, and argon.

Claims (7)

Process for preparing molecular sieve adsorbent for selective adsorption of oxygen from air, (i) exchanging zeolite X with a water-soluble salt of a rare earth metal selected from the group consisting of cerium, europium, gadolinium, and any mixtures thereof; (ii) filtering the mixture and washing the powder or pellet with hot distilled water until there are no negative ions to obtain an exchanged zeolite; (iii) drying the exchanged zeolite; And (iv) activating the exchanged zeolite; Clay and organic binders are not used. The method of claim 1, The zeolite X is characterized in that it is used in powder form or pellet form having a 100% crystallinity. The method of claim 1, Na cation of the zeolite is exchanged with salts of rare earth metals selected from chlorides, nitrates, and acetates. The method of claim 1, Wherein said cation exchange is carried out at a temperature in the range of 30 ° C. to 90 ° C. for a range of 4 to 8 hours. The method of claim 1, Said cation exchange is carried out at a cation concentration in the range of 0.01 to 0.1M solution. The method of claim 1, The exchanged zeolite is dried in a temperature range of 20 ° C. to 80 ° C. in air or under vacuum. The method of claim 1, The exchanged zeolite is activated in a temperature range of 350 ° C. to 450 ° C. for a period of 3 to 6 hours and then cooled under inert or vacuum.

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